Missing comet baffles scientists
University of Hawaii astronomers and colleagues from around the world have searched in vain for a missing comet that was supposed to appear by October.
The cosmic mystery forced the rescheduling of NASA's Extrasolar Planet Observation and Deep Impact mission to the comet 85P/Boethin. The EPOXI mission will now go to a different comet.
"We were astonished when it wasn't there," said UH astronomer Karen Meech, who led the effort to try to find Boethin.
The Subaru 9-meter telescope and 3.6-meter Canada-France-Hawaii Telescope on Mauna Kea, both with sensitive wide-field cameras, joined observatories worldwide in the futile hunt for 1-mile-long, half-mile-wide Boethin.
Although there is a chance Boethin could be observed next fall, astronomers needed to find it now to put the Deep Impact spacecraft on the right trajectory, Meech said.
Comet Hartley 2, Boethin's substitute for the $40 million mission, is just as interesting scientifically, said Tom Duxbury, EPOXI project manager at NASA's Jet Propulsion Laboratory in Pasadena, Calif. But it will take two years longer to reach, he said.
Meech said astronomers do not know what happened to comet Boethin. It is a mystery astronomers could solve next fall when the comet approaches the sun, develops a tail and gets bright, she said in an e-mail.
"It could be so far off the expected position that we didn't search far enough," Meech said, "but if that is the case, something was very unusual about the way this comet behaves."
If the missing comet is located next fall and is far off track, astronomers will try to understand why, she said.
A more likely possibility is that something caused Boethin to break apart and disintegrate, Meech said.
Boethin was discovered in 1975 and was closest to the sun in 1997, she said. It was not observed then because it was in the sky only in daylight, but it was seen in 1986, she said.
Meech was a member of the Deep Impact Science Team that planned a 2005 NASA mission that sent an 815-pound impactor crashing into Comet Tempel 1 from the spacecraft. The dust and ice from the impact were observed by the spacecraft and telescopes on Earth.
The EPOXI mission will not involve an impactor. Instead the spacecraft will fly close to Hartley 2 to take pictures and gather information about its temperature and chemistry, Meech said.
Comets are "leftover remnants" from the planet-building process in the solar system's early history, she said.
"Careful study will tell us about that process. Comets probably played a role in bringing water and organic material important for life to earth," Meech said.
Meech is in charge of characterizing the comet's physical properties to plan the EPOXI mission and will coordinate international observers for a 2010 encounter.
The spacecraft's closest approach to the half-mile-wide comet will be about 620 miles, according to NASA. Hartley 2, discovered in March 1986, has an orbital period of 6.4 years and has been observed on four trips around the sun.